Interleukin-17A
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Interleukin-17A is a protein that in humans is encoded by the IL17A gene. In rodents, IL-17A used to be referred to as CTLA8, after the similarity with a viral gene (O40633).[5][6]
Function
The protein encoded by this gene is a
Discovery
IL-17A, often referred to as IL-17, was originally discovered at transcriptional level by Rouvier et al. in 1993 from a rodent T-cell hybridoma, derived from the fusion of a mouse cytotoxic T cell clone and a rat T cell lymphoma. IL-17A receptor A (IL-17RA) was first isolated and cloned from mouse EL4 thymoma cells and the bioactivity of IL-17A was confirmed by stimulating the transcriptional factor NF-kappa B activity and interleukin-6 (IL-6) secretion in fibroblasts.[13] IL-17RA pairs with IL-17RC to allow binding and signaling of IL-17A and IL-17F.[14]
Clinical significance
High levels of this cytokine are associated with several chronic
Autoimmune diseases
Multiple sclerosis (MS) is a neurological disease caused by immune cells, which attack and destroy the myelin sheath that insulates neurons in the brain and spinal cord. This disease and its animal model experimental autoimmune encephalomyelitis (EAE) have historically been associated with the discovery of Th17 cells.[15][16] More current experiments on this animal model have also revealed that a key function of IL-17A in central nervous system (CNS) autoimmunity was to recruit IL-1β-secreting myeloid cells. These cells play a vital role in priming pathogenic Th17 cells, thus promoting the development of autoimmune disease.[17] However, elevated expression of IL-17A in multiple sclerosis (MS) lesions as well as peripheral blood has been documented before the identification of Th17 cells.[18][19] Human TH17 cells have been shown to efficiently transmigrate across the blood-brain barrier in multiple sclerosis lesions, promoting central nervous system inflammation.[20]
Th17 cells is also strongly associated rheumatoid arthritis (RA), a chronic disorder with symptoms include chronic joint inflammation, autoantibody production, which lead to the destruction of cartilage and bone.[27]
Th17 cells and IL-17 have also been linked to Crohn's disease (CD) and ulcerative colitis (UC), the two main forms of inflammatory bowel diseases (IBD). Th17 cells infiltrate massively to the inflamed tissue of IBD patients and both in vitro and in vivo studies have shown that Th17-related cytokines may initiate and amplify multiple pro-inflammatory pathways.[28] Elevated IL-17A levels in IBD have been reported by several groups.[29][30] Nonetheless, Th17 signature cytokines, such as IL-17A and IL-22, may target gut epithelial cells and promote the activation of regulatory pathways and confer protection in the gastrointestinal tract.[31][32] To this end, recent clinical trials targeting IL-17A in IBD were negative and actually showed increased adverse events in the treatment arm.[33] This data raised the question regarding the role of IL-17A in IBD pathogenesis and suggested that the elevated IL-17A might be beneficial for IBD patients.
Lung diseases
Elevated levels of IL-17A have been found in the sputum and in bronchoalveolar lavage fluid of patients with asthma[42] and a positive correlation between IL-17A production and asthma severity has been established.[43] In murine models, treatment with dexamethasone inhibits the release of Th2-related cytokines but does not affect IL-17A production.[44] Furthermore, Th17 cell-mediated airway inflammation and airway hyperresponsiveness are steroid resistant, indicating a potential role for Th17 cells in steroid-resistant asthma.[44] However, a recent trial using anti-IL-17RA did not show efficacy in subjects with asthma.[45]
Recent studies have suggested the involvement of immunological mechanisms in
Host defense
In host defense, IL-17A has been shown to be mostly beneficial against infection caused by extracellular bacteria and fungi.[51] The primary function of Th17 cells appears to be control of the gut microbiota[52][53] as well as the clearance of extracellular bacteria and fungi. IL-17A and IL-17 receptor signaling has been shown to be play a protective role in host defenses against many bacterial and fungal pathogens including Klebsiella pneumoniae, Mycoplasma pneumoniae, Candida albicans, Coccidioides posadasii, Histoplasma capsulatum, and Blastomyces dermatitidis.[54] However, IL-17A seems to be detrimental in viral infection such as influenza through promoting neutrophilic inflammation.[55]
The requirements of IL-17A and IL-17 receptor signaling in host defense were well documented and appreciated before the identification of Th17 cells as an independent T helper cell lineage. In experimental pneumonia models, IL-17A or IL-17RA knock mice have increased susceptibility to various Gram-negative bacteria, such as Klebsiella pneumoniae[56] and Mycoplasma pneumoniae.[57] In contrast, data suggest that IL-23 and IL-17A are not required for protection against primary infection by the intracellular bacteria Mycobacterium tuberculosis. Both the IL-17RA knock out mice and the IL-23p19 knock out mice cleared primary infection with M. tuberculosis.[58][59] However, IL-17A is required for protection against primary infection with a different intracellular bacteria, Francisella tularensis.[60]
Mouse model studies using the IL-17RA knock out mice and the IL-17A knock out mice with the murine adapted influenza strain (PR8)[55] as well as the 2009 pandemic H1N1 strain [93] both support that IL-17A plays a detrimental role in mediating the acute lung injury.[61]
The role of adaptive immune responses mediated by antigen specific Th17 has been investigated more recently. Antigen specific Th17 cells were also shown to recognize conserved protein antigens among different K. pneumoniae strains and provide broad-spectrum serotype-independent protection.[62] Antigen specific CD4 T cells also limit nasopharyngeal colonization of S. pneumoniae in mouse models.[63] Furthermore, immunization with pneumococcal whole cell antigen and several derivatives provided IL-17-mediated, but not antibody dependent, protection against S. pneumoniae challenge.[64][65] In fungal infection, it has been shown an IL-17 producing clone with a TCR specific for calnexin from Blastomyces dermatitidis confers protection with evolutionary related fungal species including Histoplasma spp.[66]
Cancer
In tumorigenesis, IL-17A has been shown to recruit myeloid derived suppressor cells (MDSCs) to dampen anti-tumor immunity.[67][68] IL-17A can also enhance tumor growth in vivo through the induction of IL-6, which in turn activates oncogenic transcription factor signal transducer and activator of transcription 3 (STAT3) and upregulates pro-survival and pro-angiogenic genes in tumors.[69] The exact role of IL-17A in angiogenesis has yet to be determined and current data suggest that IL-17A can promote or suppress tumor development.[70] IL-17A seemed to facilitate development of colorectal carcinoma by fostering angiogenesis via promote VEGF production from cancer cells[71] and it has been shown that IL-17A also mediates tumor resistance to anti-VEGF therapy through the recruitment of MDSCs.[72]
However IL-17A KO mice were more susceptible to developing metastatic lung melanoma,[73] suggesting that IL-17A can possibly promote the production of the potent antitumor cytokine IFN-γ, produced by cytotoxic T cells. Indeed, data from ovarian cancer suggest that Th17 cells are positively correlated with NK cell–mediated immunity and anti-tumor CD8 responses.[74]
Ocular diseases
The presence of IL-17 has been proven in a number of ocular diseases associated with neovascularization. Elevated concentration of IL-17 have been shown in vitreous fluid during proliferative diabetic retinopathy. Increased rates of Th17 cells and higher concentrations of IL-17 have been observed in patients with age-related macular degeneration.[75]
As a drug target
The discovery of the key roles of IL-17A and IL-17A producing cells in inflammation, autoimmune diseases and host defense has led to the experimental targeting of the IL-17A pathway in animal models of diseases as well as in clinical trials in humans. Targeting IL-17A has been proven to be a good approach as anti-IL-17A is FDA approved for the treatment of psoriasis in 2015.[76]
Secukinumab (anti-IL-17A) has been evaluated in psoriasis and the first report showing secukinumab is effective when compared with placebo was published in 2010.[77] In 2015, the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) approved anti-IL-17 for the treatment of psoriasis.[78]
Ixekizumab (Taltz), another anti-IL-17A,[79] was approved by the FDA[80] and the EU[81] for psoriasis in 2016. In 2017, it was approved for active psoriatic arthritis.[82]
Other than the monoclonal antibodies, highly specific and potent inhibitors targeting Th17 specific transcription factor RORγt have been identified and found to be highly effective.[83]
Vitamin D, a potent immunomodulator, has also been shown to suppress Th17 cell differentiation and function by several research groups.[84] The active form of vitamin D has been found to 'severely impair'[85] production of the IL17 and IL-17F cytokines by Th17 cells.
See also
Notes
Wikidata Q39103136 . |
References
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Further reading
- Gaffen SL (2005). "Biology of recently discovered cytokines: interleukin-17--a unique inflammatory cytokine with roles in bone biology and arthritis". Arthritis Research & Therapy. 6 (6): 240–247. PMID 15535837.
- Lubberts E, Koenders MI, van den Berg WB (2006). "The role of T-cell interleukin-17 in conducting destructive arthritis: lessons from animal models". Arthritis Research & Therapy. 7 (1): 29–37. PMID 15642151.
- Fossiez F, Djossou O, Chomarat P, Flores-Romo L, Ait-Yahia S, Maat C, et al. (June 1996). "T cell interleukin-17 induces stromal cells to produce proinflammatory and hematopoietic cytokines". The Journal of Experimental Medicine. 183 (6): 2593–2603. PMID 8676080.
- Yao Z, Spriggs MK, Derry JM, Strockbine L, Park LS, VandenBos T, et al. (November 1997). "Molecular characterization of the human interleukin (IL)-17 receptor". Cytokine. 9 (11): 794–800. PMID 9367539.
- Murphy KP, Gagne P, Pazmany C, Moody MD (March 1998). "Expression of human interleukin-17 in Pichia pastoris: purification and characterization". Protein Expression and Purification. 12 (2): 208–214. PMID 9518462.
- Teunissen MB, Koomen CW, de Waal Malefyt R, Wierenga EA, Bos JD (October 1998). "Interleukin-17 and interferon-gamma synergize in the enhancement of proinflammatory cytokine production by human keratinocytes". The Journal of Investigative Dermatology. 111 (4): 645–649. PMID 9764847.
- Shalom-Barak T, Quach J, Lotz M (October 1998). "Interleukin-17-induced gene expression in articular chondrocytes is associated with activation of mitogen-activated protein kinases and NF-kappaB". The Journal of Biological Chemistry. 273 (42): 27467–27473. PMID 9765276.
- Shin HC, Benbernou N, Fekkar H, Esnault S, Guenounou M (November 1998). "Regulation of IL-17, IFN-gamma and IL-10 in human CD8(+) T cells by cyclic AMP-dependent signal transduction pathway". Cytokine. 10 (11): 841–850. PMID 9878122.
- Laan M, Cui ZH, Hoshino H, Lötvall J, Sjöstrand M, Gruenert DC, et al. (February 1999). "Neutrophil recruitment by human IL-17 via C-X-C chemokine release in the airways". Journal of Immunology. 162 (4): 2347–2352. S2CID 12318929.
- Kotake S, Udagawa N, Takahashi N, Matsuzaki K, Itoh K, Ishiyama S, et al. (May 1999). "IL-17 in synovial fluids from patients with rheumatoid arthritis is a potent stimulator of osteoclastogenesis". The Journal of Clinical Investigation. 103 (9): 1345–1352. PMID 10225978.
- Shin HC, Benbernou N, Esnault S, Guenounou M (April 1999). "Expression of IL-17 in human memory CD45RO+ T lymphocytes and its regulation by protein kinase A pathway". Cytokine. 11 (4): 257–266. PMID 10328864.
- Andoh A, Takaya H, Makino J, Sato H, Bamba S, Araki Y, et al. (July 2001). "Cooperation of interleukin-17 and interferon-gamma on chemokine secretion in human fetal intestinal epithelial cells". Clinical and Experimental Immunology. 125 (1): 56–63. PMID 11472426.
- Laan M, Palmberg L, Larsson K, Lindén A (March 2002). "Free, soluble interleukin-17 protein during severe inflammation in human airways". The European Respiratory Journal. 19 (3): 534–537. PMID 11936535.
- Andoh A, Fujino S, Bamba S, Araki Y, Okuno T, Bamba T, Fujiyama Y (August 2002). "IL-17 selectively down-regulates TNF-alpha-induced RANTES gene expression in human colonic subepithelial myofibroblasts". Journal of Immunology. 169 (4): 1683–1687. PMID 12165487.
- Andoh A, Shimada M, Bamba S, Okuno T, Araki Y, Fujiyama Y, Bamba T (August 2002). "Extracellular signal-regulated kinases 1 and 2 participate in interleukin-17 plus tumor necrosis factor-alpha-induced stabilization of interleukin-6 mRNA in human pancreatic myofibroblasts". Biochimica et Biophysica Acta (BBA) - Molecular Cell Research. 1591 (1–3): 69–74. PMID 12183057.
- Hsieh HG, Loong CC, Lin CY (August 2002). "Interleukin-17 induces src/MAPK cascades activation in human renal epithelial cells". Cytokine. 19 (4): 159–174. PMID 12297109.
- Aggarwal S, Ghilardi N, Xie MH, de Sauvage FJ, Gurney AL (January 2003). "Interleukin-23 promotes a distinct CD4 T cell activation state characterized by the production of interleukin-17". The Journal of Biological Chemistry. 278 (3): 1910–1914. PMID 12417590.
External links
- Overview of all the structural information available in the PDB for UniProt: Q16552 (Interleukin-17A) at the PDBe-KB.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.